ClaimEscalationResult: {
    entry: EscalationEntry;
    isExtension: boolean;
    ok: true;
} | {
    ok: false;
    reason: "not-found" | "conflict";
}

Result of claim() — identifies whether failure was due to the row not existing (not-found) or existing but locked / in a non-claimable state (conflict). Distinguishing these lets callers decide whether to retry or surface an error to the user.